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Underground pneumatic boring is used to bore an underground hole between two points without disturbing the surface. The tools are often referred to as a hog, air hog, or pneuma gopher. This open-air chamber is referred to as the borehole and is used to either run ducting for a product or the product itself between two points.
Uses edit
Underground pneumatic drills are used in the installation of all public utilities electricity, gas, phone, and cable television; these are referred to as products. It is also used to install residential lawn irrigation systems and auxiliary home power lines. Boring is utilized in instances when it is difficult or cost-prohibitive to plow or trench the product into the ground. Some of these instances are under driveways, roads, sidewalks, and landscaping.
Underground pneumatic boring is typically a low-cost alternative to directional boring.
Process edit
Underground pneumatic drill uses compressed air to bore its way through the ground underneath obstructions. The tool is cylindrical and ranges from one to eight inches in diameter and between three and six feet long. It is made from metal, typically steel. Manufacturers have different font styles and control mechanisms. The compressed air is run through a hydraulic hose with an oiler attachment to send oil through with the compressed air, akin to a jackhammer.
Inside the cylinder is a piston. A valve opens and the air blows into the chamber, forcing the piston forward, which in turn propels the tool forward. The valve then shuts, and the piston is pushed at a slower speed back into the tool. The valve reopens, the piston pounds again, and the tool moves forward. This process is continually repeated until the drill has run the intended distance. Both the lighter reverse hit of the piston and the friction of the ground surrounding the tool keep it moving forward instead of stopping. The speed of the tool can be controlled by a valve that connects the tool's hose to the air supply. This valve is outside the tool and remains accessible to the operator. As the tool pounds through the ground, it compresses the soil. This compaction maintains the same diameter as the tool and leaves the borehole through which the product is passed.
Boring edit
The purpose of the drill is to create a tunnel under surface obstructions. First, the operator surveys the area and the obstacle (road, sidewalk, driveway). Utility locators must supervise any underground work, and the path most clear of utilities is chosen to send the tool through. The first hole is dug on one side of the obstacle. This hole must be large enough to fit the tool and the operator to aim the tool. The hole also must be deep enough that, as the tool compacts the ground, the surface remains undisturbed. The depth of the starting bore pit depends on the type of soil that is being worked in and how well it compacts. The operator aims the tool to the desired exit point and allows it to perform its function, creating a borehole under the ground without disturbing the surface. The tool is tracked by the operator, who feels the tool pounding and can approximate the tool's location under the ground. The operator also monitors the surface to make sure that it is undisturbed. As the tool nears the exit point it is slowed down and an exit pit is dug to locate both the tool and the bore. As the tool enters the exit pit the operator chooses to either dig up the tool to retrieve it or reverse the tool back into the first bore pit to retrieve it. Now between the two pits is a completed bore under the obstacle which can be used to run the product.
Disadvantages edit
Pneumatic drill tools do have drawbacks which can cause difficulties completing the bore. First, the distance of the drill is limited by the length of the hose that supplies the tool with air. Also, the tool is not steerable. Once it has exited the bore pit, the operator no longer has control over it. The tool can be deflected by rocks and soil density to a path the operator had not intended. If this deflection is in the direction of the surface, the tool can cause damage to the obstacle being bored. One more drawback is that the tool can dive to an unrecoverable depth. If it is deflected side to side the tool could also run into other utilities. These hazards make it important for the operator to maintain close observation of the tool. The type of ground on which drill works can also lead to problems. If the soil is too loose, the tool cannot compact the soil, stalling it out or leaving no borehole. If the soil is rocky the tool may be deflected or fail to pound forward due to its inability to break the rock. These drawbacks can be overcome by directional boring or straight-line horizontal underground boring machines that use either wet (slick boring, slurry boring) or dry (auger boring, jack and bore) methods.